1. Field
Aspects of embodiments according to the present invention relate to an organic light emitting display device.
2. Description of Related Art
Recently, there have been developed various types of flat panel display devices having less weight and volume than that of a comparable cathode ray tube device. The flat panel display devices include liquid crystal display devices, field emission display devices, plasma display panels, organic light emitting display devices, and the like.
Among these flat panel display devices, the organic light emitting display device displays images using organic light emitting diodes (OLEDs) that emit light through recombination of electrons and holes. The organic light emitting display device has a fast response speed and is driven with low power consumption.
An organic light emitting display device has a plurality of pixels arranged in a matrix form at crossing regions of data lines, scan lines, and power lines. Each of the pixels usually includes an organic light emitting diode (OLED), two or more transistors including a driving transistor, and one or more capacitors.
Such an organic light emitting display device has low power consumption. However, in a typical organic light emitting display device, the amount of current that flows to each OLED varies depending on the threshold voltage of the driving transistor included in each pixel. Therefore, images with unequal luminance are displayed. That is, characteristics of the driving transistors vary between pixels depending on factors such as the fabrication process. From a practical standpoint, it is impossible with current fabrication processes to fabricate the organic light emitting display device so that all of the transistors of the organic light emitting display device have the same characteristics. Therefore, the variation in the threshold voltage of the driving transistors occurs.
To solve such a problem, there has been proposed a method of adding a compensation circuit including a plurality of transistors and capacitors to each of the pixels. The compensation circuit included in each of the pixels stores a voltage corresponding to the threshold voltage of the driving transistor. Accordingly, the variation in the threshold voltage of the driving transistor is compensated.
To help remove motion blur, recent methods of driving a driving transistor at a driving frequency of over 120 Hz have been developed. However, when the driving transistor is driven at such a high frequency, the period for storing the threshold voltage of the driving transistor is shortened. Therefore, it is not possible to sufficiently compensate the threshold voltage of the driving transistor.